Maize resistant to aryloxyphenoxyalkanecarboxylic acid herbicides

ABSTRACT

By selection for resistance to aryloxyphenoxyalkanecarboxylic acid herbicides, herbicide-tolerant maize cell lines, calli and plants regenerated therefrom can be obtained which pass this herbicide tolerance on to their progeny in a stable manner.

This application is a division of application Ser. No. 08/245,064, filedMay 17, 1994, now abandoned, which is a continuation of Ser. No.08/070,430, filed Jun. 8, 1993, now abandoned, which is the NationalPhase of PCT/EP92/00506, filed Mar. 7, 1992, designating the U.S.

BACKGROUND OF THE INVENTION

Aryloxyphenoxyalkanecarboxylic acid herbicides (which are also to beunderstood as meaning heteroaryloxyphenoxyalkanecarboxylic acidderivatives) are effective grass herbicides. A representative of thisclass of active substances which is to be mentioned hereinafter isfenoxaprop-ethyl ("FOPE"), which is to be understood as meaning thebiologically active D-isomer as well as the racemate. They act on plantsfrom the family of the Poaceae (Gramineae), since only this plant familyhas a specific form of acetyl coenzyme A carboxylase (ACC) which can beinhibited by micromolar concentrations of FOPE. Remaining terrestrialplants have ACC types whose sensitivity to this class of activesubstances is 100 to 1000 times lower.

Since FOPE and other aryloxyphenoxyalkanecarboxylic acid herbicides aretaken up via the aerial parts of the plants, but are rapidly inactivatedin the soil, these herbicides are suitable for controlling grassespost-emergence.

The crop plant maize (Zea mays) is particularly sensitive to FOPE. Thisis why these compounds cannot be used for controlling grass weeds inmaize fields.

It has been found that in areas where FOPE has been applied repeatedly,forms arise spontaneously in populations of wild grasses which areresistant to this class of herbicide. Since such mutations occur only ata rate of approximately 10⁻⁷ to 10⁻⁹, a corresponding search for mutantsin maize fields would be of little promise even if maize were not sohighly sensitive to FOPE.

SUMMARY OF THE INVENTION

Surprisingly, it has now been found that maize cells can be selectedwhich are resistant to FOPE and which can be grown on to give resistantplants which, in turn, pass on this resistance property in a stablemanner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Cell lines which are suitable for selection are known (for example fromMorocz et al., Theor. Appl. Genet. 80 (1990) 721-726) or have beenproposed in European Patent Applications 90 111 945.3 and 90 111 946.1.With effect from Sep. 30, 1990, a suitable cell line was deposited atthe Deutsche Sammlung yon Mikroorganismen und Zellkulturen [GermanCollection of Microorganisms and Cell Cultures] in compliance with theprovision of the Budapest treaty, Deposit No. DSM 6009.

To obtain resistant cell lines, the cells are cultured in auxin-freemedia in the presence of FOPE concentrations which kill more than 90% ofthe cells. The cells can be cultured in such media for as long asdesired, for example easily over 10 transfers and more. Syntheticauxins, such as 2,4-dichlorophenoxyacetic acid, p-chlorophenoxyaceticacid, 2,4,5-trichlorophenoxyacetic acid and3,6-dichloro-2-methoxybenzoic acid (dicamba) antagonize the effect ofFOPE if the latter is employed in sublethal concentrations. Selectionexperiments using FOPE in the concentration range of up to 10⁻⁵ M in thepresence of synthetic auxins were unsuccessful. This is whyauxin-autotrophic maize cell lines were used.

It is characteristic of auxin-autotrophic cell lines that they can, inthe form of an embryogenic culture, be subcultured on phytohormone-freecell culture media for as long as desired, for example for two to threeyears. Auxin-autotrophic calli were subcultured in each case every 3 to4 weeks over 15 transfers and more, and mutants were found by stepwiseincrease of the FOPE concentration. These FOPE-tolerant mutants can besub-cultured over 10 transfers and more on FOPE-containing, auxin-freemedium. Under selective conditions, i.e. in the presence of 10⁻⁴ M FOPE,the embryogenic calli spontaneously give rise to plants which can begrown on to give fertile maize plants.

Flowering regenerated plants are, on the one hand, selfed and, on theother hand, pollen from the regenerated plants is used for pollinatinginbred lines. The mature seeds are sown, and the F₁ generation seedlingsare treated with FOPE when they have reached the 2- to 4-leaf stage. Aconsiderable number of selected plants survive even at concentrations ofup to 200 g of active substance per ha (g of a.i./ha).

The regenerated maize plants can be treated with FOPE at rates of up to200 g of a.i./ha; it is preferred to employ between 20 and 150 g, inparticular between 30 and 90 g, of a.i./ha. These amounts apply to thebiologically active D-isomer of fenoxaprop-ethyl. Maize plants accordingto the invention are preferably selected using the optically activeisomer, but suitable amounts of the racemate can also be employed.

The ACC gene can be isolated from the mutants according to the inventionand characterized in a manner known per se. Mutated genes, which encodeFOPE-tolerant ACC, can be used for the transformation of other plantcells.

It is furthermore possible to combine FOPE tolerance in maize withresistance to other herbicides. To this end, for example, transgeniccell lines are used which contain a resistance gene for thenon-selective herbicide phosphinothricin, glufosinate or bialaphos. Suchgenes are disclosed, for example, in EP-A 0,257,542, 0,275,957,0,297,618 or from DE-A 3,701,623 or DE-B 3,825,507. When suitable celllines are grown, phosphinothricin tolerance can be employed as anadditional marker.

Other transgenic plants according to the invention may contain toxingenes, for example genes encoding the δ-endotoxin of Bacillusthuringiensis, or genes for chitinases or glucanases, or otherselectable marker genes, for example genes for resistance to glyphosateor sulfonylureas.

The following (C₁ -C₄)alkyl, (C₂ -C₄)alkenyl and (C₃ -C₄)alkynylaryloxyphenoxyalkanecarboxylate herbicides can also be employed forselecting resistant maize cell lines:

A1) Phenoxyphenoxy- and benzyloxyphenoxyalkanecarboxylic acidderivatives, for example

methyl 2-(4-(2,4-dichlorophenoxy)phenoxy)propionate (diclofop-methyl),

methyl 2-(4-(4-bromo-2-chlorophenoxy)phenoxy)propionate (seeDE-A-2,601,548),

methyl 2-(4-(4-bromo-2-fluorophenoxy)phenoxy)propionate (see U.S. Pat.No. 4,808,750),

methyl 2-(4-(2-chloro-4-trifluoromethylphenoxy)phenoxy)propionate (seeDE-A-2,433,067),

methyl 2-(4-(2-fluoro-4-trifluoromethylphenoxy)phenoxy)propionate (seeU.S. Pat. No. 4,808,750),

methyl 2-(4-(2,4-dichlorobenzyl)phenoxy)propionate (see DE-A-2,417,487),

ethyl 4-(4-(4-trifluoromethylphenoxy)phenoxy)pent-2-enoate,

methyl 2-(4-(4-trifluoromethylphenoxy)phenoxy)propionate (seeDE-A-2,433,067),

A2) "Mononuclear" heteroaryloxyphenoxyalkanecarboxylic acid derivatives,for example

ethyl 2-(4-(3,5-dichloropyridyl-2-oxy)phenoxy)propionate (seeEP-A-2,925),

propargyl 2-(4-(3,5-dichloropyridyl-2-oxy)phenoxy)propionate(EP-A-3,114),

methyl 2-(4-(3-chloro-5-trifluoromethyl-2-pyridyloxy)phenoxypropionate(see EP-A-3,890),

ethyl 2-(4-(3-chloro-5-trifluoromethyl-2-pyridyloxy)phenoxy)propionate(see EP-A-3,890),

propargyl 2-(4-(5-chloro-3-fluoro-2-pyridyloxy)phenoxy)propionatepropionate (EP-A-191,736),

butyl 2-(4-(5-trifluoromethyl-2-pyridyloxy)phenoxypropionate(fluazifop-butyl; fusilade-butyl),

A3) "Binuclear" heteroaryloxyphenoxyalkanecarboxylic acid derivatives,for example

methyl and ethyl 2-(4-(6-chloro-2-quinoxalyloxy)phenoxy)propionate(quizalofop-methyl and -ethyl),

methyl 2-(4-(6-fluoro-2-quinoxalyloxy)phenoxy)propionate (see J. Pest.Sci. Vol. 10, 61 (1985)),

methyl and 2-isopropylideneaminooxyethyl2-(4-(6-chloro-2-quinolyloxy)phenoxy)propionate (propaquizafop and itsester),

ethyl 2-(4-(6-chlorobenzoxazol-2-yloxy)phenoxy)propionate(fenoxaprop-ethyl) and

ethyl 2-(4-(6-chlorobenzothiazol-2-yloxy)phenoxypropionate (seeDE-A-2,640,730)).

The auxin-autotrophic cell lines are also particularly suitable for theselection of mutants which are obtained using other ACC-inhibitors,namely cyclohexanedione-herbicides, in particular sethoxydim,tralkoxydim, cycloxydim, alloxydim and clethoxydim.

The fact that maize plants can be obtained which are resistant toconventional concentrations of sethoxydim has been published by Parkeret al. (Proc. Natl. Acad. Sci. Vol. 87, pp. 7175-7179). These plantsalso display a certain cross-resistance to low concentrations ofhaloxyfop. However, the maize plants produced according to the inventionare resistant to higher concentrations of aryloxyphenoxyalkanecarboxylicacid herbicides, as they are required for use in practice. Thus, themaize plants according to the invention allow the selective control ofmonocotyledon weeds (grass weeds) in maize usingaryloxyphenoxyalkanecarboxylic acid derivatives (includingheteroaryloxyphenoxyalkanecarboxylic acid derivatives), either alone orin combination with each other.

The invention also relates to the use of maize plants which are treatedwith a combination of aryloxyphenoxycarboxylic acid herbicides andherbicides against dicotyledon weeds. This is because it was possible,surprisingly, to identify components for mixtures foraryloxyphenoxyalkanecarboxylic acid herbicides which are not onlytolerated by the regenerated maize plants, but whose herbicidal activityis simultaneously improved.

Thus, the combination of the herbicides results in synergistic effects.Using such mixtures means substantial economical, but also ecological,advantages.

Synergism is to be understood as meaning a mutually reinforcing effectof two or even more substances. In the present case, the combined use oftwo herbicides allows the application rate of the herbicides to bereduced while still achieving the same herbicidal activity, or, usingthe same application rates of the herbicides allows a higher activity tobe achieved than to be expected on the basis of the individuallyemployed active substances.

By using such synergistic effects, it is possible to considerably reducethe application rates of the components involved in the mixture, and abroad range of mono- and dicotyledon weeds can be controlled in oneoperation. The reduced application rates apply in particular to theACC-inhibitors, but also to the components in the mixtures with regardto effectiveness against dicotyledon weeds.

Particularly interesting from amongst the aryloxyphenoxyalkanecarboxylicacid herbicides are the following herbicides: fenoxaprop-ethyl,haloxyfop-methyl, quizalofop-ethyl, fluazifop-butyl.

The following herbicides display synergistic activity when used as acomponent in mixtures for the additional control of broad-leaf weeds:

Primisulfuron, thifensulfuron, nicosulfuron, DPX-E 9636, amidosulfuron,pyridylsulfonylureas, as described in German Patent Applications P4,000,503.8 and P 4,030,577.5, in particular3-(4,6-dimethoxypyrimidin-2-yl)-1-[3-(N-methyl-N-methylsulfonylamino-2-pyridylsulfonyl]urea,an alkoxyphenoxysulfonylurea, as described in EP-A-0,342,569,furthermore NC 319 (EP 282,613) and other sulfonylureas, as well asmixtures of various abovementioned sulfonylureas with each other, suchas, for example, a mixture of nicosulfuron and DPX-E 9636.

Other herbicides which have the same, or a similar, mechanism of actionas the above sulfonylureas, namely imidazolinones, such as, for example,imazethapyr, imazaquin, imazapyr (each of which can be employed in maizetogether with a safener), also display a synergistic increase inactivity when employed together with ACC inhibitors.

Other herbicides which, like sulfonylureas and imidazolinones, areinhibitors of the enzyme acetolactate synthase (ALS) are also suitable,for example substituted pyrimidines and triazines, herbicidalsulfonamides, such as flumetsulam (Cordes, R. C. et al., Abstr. Meet.Weed Sci. Soc. Am. 31, 10, 1991), or other related compounds andmixtures of such active substances with each other.

A series of other herbicides which are employed for controlling weeds inmaize, but display different mechanisms of action, also showed asynergistic increase in activity when used together withfenoxaprop-ethyl or with other ACC inhibitors:

ICI-051: (2-[2-chloro-4-(methylsulfonyl)benzoyl]-1,3-cyclohexanedione,atrazine, cyanazine and terbuthylazine, clopyralid, pyridate,bromoxynil, pendimethalin, dicamba.

The herbicides are generally used at application rates of between 0.01and 2 kg/ha, i.e. the total amount of active substance combination to beused is approximately 0.05 to 2 kg/ha. The application rate required canvary as a function of the external conditions, such as temperature andhumidity, inter alia, that is preferably between 0.05 and 1 kg/ha. Theratios of the components can vary within wide limits. A quantitativeratio of between 1:20 and 20:1 is preferably selected.

These synergistic effects are achieved not only in the case of mixtureswith fenoxaprop-ethyl, but also when other ACC inhibitors are used, forexample the cyclohexanediones. A combination of the active substances isto be understood as meaning that the herbicidal active substances areapplied together or one after the other, at an interval of a few days,in the form of a so-called split application. In each case the weedsrespond with an increased sensitivity, so that lower application ratesallow a very good control effect.

In the following examples, the invention will be illustrated in greaterdetail without being restricted thereto. Percentages relate to theweight, unless otherwise specified.

EXAMPLE 1 Selection of FOPE-tolerant Embryogenic Maize Cell Cultures

Maize plants from inbred lines B 73 and LH 82 were pollinated withpollen from genotype HE 89, which is capable of regeneration (Morocz etal., Theor. Appl. Genet. 80 (1990) 721-726 loc. cit.). 12 to 14 daysafter pollination, immature embryos were dissected from the seeds understerile conditions and grown on hormone-free N₆ culture medium (Chu etal., Sci. Sin. 18 (1975) 659-668) containing 9% of sucrose, the embryoaxis being in contact with the medium. Within 3 to 4 weeks, embryogeniccallus was formed on approximately 25% of the embryos, 1.0 to 2.0 mm insize, and this embryogenic callus could be subcultured on hormone-freemedium. After 3 to 4 subcultures, the selection of FOPE-tolerant mutantswas started using the callus lines which were distinguished by vigorousgrowth and reproducible differentiation of somatic embryos on thehormone-free medium.

Alternatively, callus lines were cultured, with 3 to 4 transfers, on N₆medium containing 1 mg/l of 2,4-dichlorophenoxyacetic acid (2,4-D). Thecallus sectors consisting of undifferentiated cells were used forsubculturing. From these callus sectors, suspension cultures could beinduced which were cultured in liquid N₆ medium containing 0.5 mg/l of2,4-D and transferred weekly to fresh medium.

Tissue was taken from both callus cultures and suspension cultures andincubated for 4 to 6 weeks on hormone-free N₆ medium in the presence of1-3×10⁻⁶ M FOPE. Under these conditions, up to approximately 95% of thecells and cell clusters were killed.

The surviving cell clusters were grown on on hormone-free N₆ mediumcontaining 3×10⁻⁶ M FOPE, by means of 2 transfers. Per transfer, thecells remained on the selection medium for 4 to 6 weeks.

Subclones growing equally well under these conditions as wild-type cellson FOPE-free medium were grown on on hormone-free N₆ medium containing1×10⁻⁵ M FOPE.

After a further 4 to 6 weeks, those clones which continued to grow onthis selection medium without significant loss of vitality weretransferred to a medium containing 3×10⁻⁵ M FOPE and, during thefollowing subculturing, transferred to hormone-free N₆ medium containing1×10⁻⁴ M active substance. Higher active substance concentrations didnot improve the selection effect further since the active substancecrystallizes in the medium at a concentration of as little as 3×10⁻⁵ M.

EXAMPLE 2 Regeneration of FOPE-tolerant Plants

Plants which have been regenerated from those mutated clones which grewin the presence of 1×10⁻⁴ N FOPE in hormone-free N₆ medium for 3 to 10transfers without reduced vitality, differentiating plants from somaticembryos in the process, were transferred into soil and grown in acontrolled-environment cabinet at 30,000 to 40,000 Lux, a daytimetemperature of 23°±1° C. and a night-time temperature of 16°±1° C., withan illumination period of 14 hours. When the plants have developed 4 to5 leaves, they are sprayed with 30 g of FOPE per ha. The plants survivedthis treatment without significant damage, while control plantswere-killed by the herbicide at this dosage rate.

The flowering regenerated plants were, on the one hand, selfed and, onthe other hand, their pollen was used for pollinating inbred lines, suchas, for example, B 73, LH 51, LH 82, LH 119, KW 1292, KW 5361, RA 1298or RA 3080. The mature seeds were sown, and the F₁ generation seedlingstreated with FOPE when they had reached the 2- to 4-leaf stage. Theresults are given in Table 1.

                  TABLE 1                                                         ______________________________________                                        Treatment of regenerated plants and progeny                                   with FOPE (* und. = undamaged)                                                            FOPE treatment                                                                      15 g of   30 g of 60 g of                                                     a.i./ha dead                                                                            a.i./ha dead                                                                          a.i./ha dead                                                plants/   plants/ plants/                                   Plants   Number   und.*     und.*   und.*                                     ______________________________________                                        Regen.   20                   20   --                                         plants of                                                                     unselected                                                                    controls                                                                      Regen.   10                   --   10                                         plants of                                                                     resistant                                                                     callus                                                                        Progeny from                                                                           60       5      15    7   13   8    12                               self-pollin-                                                                           (3 × 20)                                                       ation                                                                         F.sub.1 -progeny                                                                       48       8       8   10    6   7    9                                from     (3 × 16)                                                       crosses                                                                       Commercial                                                                             48       16     --   16   --   16   --                               variety                                                                       Felix                                                                         ______________________________________                                    

EXAMPLE 3 Haloxyfop-tolerant Maize

Resistant maize cell lines were obtained by the process described inExamples 1 and 2 and examined for resistance to haloxyfop. It was foundthat cell lines according to the invention tolerate a markedly higherdosage rate than the maize cell lines known from the prior art (seeParker et al.).

EXAMPLE 4 Treatment of Herbicide-resistant Maize Plants with SynergisticCombinations of Herbicides

FOPE-resistant maize plants obtained by the process described inExamples 1 and 2 were grown in the greenhouse in pots of diameter 9 cmtogether with grass weeds and broad-leaf weeds until they had reachedthe 4-6 leaf stage, when they were treated post-emergence with theherbicides according to the invention. A water volume of 400 l/ha wasused, two replications were carried out, and, after 5 weeks, the plantswere scored on a percentage key basis by visually assessing the controleffect on the weeds.

The results from various experiments showed unexpected synergisticincreases in effects by herbicidal combinations which had been appliedeither concomitantly or one shortly after the other (see Tables 2 and3).

No damage of any kind was observed on the herbicide-resistant maizeplants. Herbicides B4 and B6 were in each case both applied togetherwith an active substance which acts as a safener.

                                      TABLE 2                                     __________________________________________________________________________    Herbicidal activity against grasses                                           __________________________________________________________________________          Dosage rate of                                                                        % activity against                                              Herbicide                                                                           g of AS/ha                                                                            SEVI                                                                              DISA                                                                              PAMI ECCG                                                                              SOHA                                                                              ZEMA                                       __________________________________________________________________________    A     50      100 100 --   --  --  0                                                25      100 99  100  100 98  0                                                12      85  85  100  100 85  0                                                6       60  50  80   99  40  0                                          B1    50      98  93  65   98  60  0                                                25      95  85  20   95  35  0                                                12      85  75  10   80  25  0                                          B2    12      0   10  0    0   20  0                                                6       0   5   0    0   0   0                                          B3    50      50  20  30   30  90  0                                                25      40  10  0    20  80  0                                                12      30  0   0    20  70  0                                          B4    25      80  90  65   95  45  0                                                12      70  85  40   90  30  0                                                6       60  70  15   75  20  0                                          B5    25      85  95  70   90  70  0                                                12      80  90  40   80  50  0                                                6       80  80  25   70  30  0                                          B6    100     95  90  70   70  60  0                                                50      80  80  60   70  40  0                                          B7    250     5   0   0    10  0   0                                                125     0   0   0    0   0   0                                          B8    250     0   0   0    0   0   0                                                125     0   0   0    0   0   0                                          B9    250     0   0   0    5   0   0                                                125     0   0   0    0   0   0                                          A + B1                                                                              12 + 12 100 100 100  100 98  0                                                12 + 25 100 98  95   100 80  0                                          A + B2                                                                              12 + 12 100 100 100  100 99  0                                                 6 + 12 100 99  100  100 75  0                                          A + B3                                                                              12 + 12 100 100 100  100 100 0                                                12 + 25 100 100 100  100 100 0                                          A + B4                                                                              12 + 12 100 100 100  100 99  0                                                6 + 6   100 95  95   100 90  0                                          A + B5                                                                              12 + 12 100 100 100  100 100 0                                                6 + 6   100 98  98   100 100 0                                          A + B6                                                                              12 + 50 100 100 100  100 100 0                                                 6 + 25 100 99  98   100 95  0                                          A + B7                                                                               12 + 125                                                                             95  90  100  100 95  0                                          A + B8                                                                               12 + 125                                                                             90  95  100  99  90  0                                          A + B9                                                                               12 + 125                                                                             95  90  99   99  90  0                                          __________________________________________________________________________          Dosage rate of                                                          Herbicide                                                                           g of AS/ha                                                                            ABTH                                                                              CHAL                                                                              AMAR POCO                                                                              AMRE                                                                              ZEMA                                       __________________________________________________________________________    A     50      0   0   0    0   5   0                                                25      0   0   0    0   0   0                                                12      0   0   0    0   0   0                                                6       0   0   0    0   0   0                                          B1    50      20  35  20   50  60  0                                                25      10  20  10   30  50  0                                                12      0   10  0    10  50  0                                          B2    12      40  80  70   80  20  0                                                6       20  60  40   50  10  0                                          B3    50      70  80  30   40  40  0                                                25      50  70  10   20  30  0                                                12      40  50  0    20  15  0                                          B4    25      20  95  85   80  80  0                                                12      10  85  80   70  75  0                                                6       0   50  70   70  60  0                                          B5    25      30  80  75   30  60  0                                                12      20  60  60   20  50  0                                                6       10  40  40   10  30  0                                          B6    100     60  40  70   50  80  0                                                50      50  30  60   40  70  0                                          B7    250     40  100 75   80  75  0                                                125     15  85  40   50  30  0                                          B8    250     70  95  70   85  65  0                                                125     30  75  30   60  30  0                                          B9    250     90  100 98   80  75  0                                                125     75  80  70   40  60  0                                          A + B1                                                                              12 + 12 40  50  30   60  90  0                                                12 + 25 40  30  30   40  75  0                                          A + B2                                                                              12 + 12 70  90  80   95  40  0                                                 6 + 12 60  80  75   90  40  0                                          A + B3                                                                              12 + 12 60  70  30   50  30  0                                                12 + 25 70  80  40   50  40  0                                          A + B4                                                                              12 + 12 50  95  90   90  80  0                                                6 + 6   30  60  80   90  75  0                                          A + B5                                                                              12 + 12 50  90  95   40  90  0                                                6 + 6   40  75  50   30  60  0                                          A + B6                                                                              12 + 50 70  50  95   70  80  0                                                 6 + 25 50  30  60   40  60  0                                          A + B7                                                                               12 + 125                                                                             40  90  50   70  50  0                                          A + B8                                                                               12 + 125                                                                             60  80  40   60  40  0                                          A + B9                                                                               12 + 125                                                                             90  90  80   50  60  0                                          __________________________________________________________________________

Key for Table

SEVI=Setaria viridis (green foxtail)

DISA=Digitaria sanguinalis (large crab grass)

PAMI=Panicum miliaceum (proso millet)

ECCG=Echinochloa crus galli (common barnyard grass)

SOHA=Sorghum halepense (Johnson grass)

ABTH=Abutilon theophrasti (velvetleaf)

CHAL=Chenopodium album (pigweed)

AMAR=Ambrosia artemisifolia (hogweed)

POCO=Polygonum convolvulus (black bindweed)

AMRE=Amaranthus retroflexus (red root pigweed)

ZEMA=Zea mays (maize)

A=Fenoxaprop-p-ethyl

B2=Nicosulfuron

B2=Thifensulfuron

B3=Primisulfuron

B4=3-(4,6-Dimethoxypyrimidin-2-yl)-1-[3-(N-methyl-N-methylsulfonylamino)-2-pyridylsulfonyl]urea

B5=DPX-9636

B6=Imazethapyr

B7=Atrazine

B8=Bromoxynil

B9=Dicamba

I claim:
 1. A method for controlling mono- and dicotyledon weeds incultures of maize plants which are resistant toaryloxyphenoxyalkanecarboxylic acid herbicides comprising applying tosaid plants aryloxyphenoxyalkanecarboxylic acid herbicides incombination with one or more herbicides selected from the group of thesulfonylureas and imidazolinones.
 2. A method for controlling mono- anddicotyledon weeds in cultures of maize plants which are resistant toaryloxyphenoxyalkanecarboxylic acid herbicides comprising applying tosaid plants fenoxaprop-ethyl in combination with a sulfonylurea.
 3. Amethod for controlling mono- and dicotyledon weeds in cultures of maizeplants which are resistant to aryloxyphenoxyalkanecarboxylic acidherbicides comprising applying to said plants fenoxaprop-ethyl incombination with one or more herbicides selected from the group of thetriazines, clopyralid, pyridate, bromoxynil, pendimethalin and dicamba.